This invention relates to a sheet deliverer for a sheet processing machine, particularly a sheet printing machine with high stapling or stacking delivery in which the sheets are taken off the machine by means of controlled gripper pads carried on orbitally moveable chains (e.g., roller chains), and are conveyed thereby to a stapling or stacking table upon which the sheets are delivered and stapled (i.e., stacked) to a high staple, wherein a plurality of the gripping pads are disposed parallel to each other in laterally spaced relation and are fastened to the respective laterally spaced rotating or orbiting chains which travel in chain guides with upper and lower guide flanks, and wherein the chain guides are guided at the input and the output sides of the sheet deliverer over reversing guides or wheels, and the chain guides extend at least from an input reversing guide to the upper side of the stapling table.
Sheet deliverers having the above described features are known in numerous embodiments. They all are arranged such that the chain guide way forms a generally Z-like or S-like path of travel for the chains in side view, which constrains the chains guided thereby to proceed through repeated changes of direction in their traverse of the chain guides. One example of such an apparatus is disclosed in German patent specification 23 08 025.
A different prior art sheet deliverer described in German patent specification 25 44 566 also provides in the lower and upper chain guide ways several changes of direction of chain movement including straight or flat chain runs where the chain is not positively engaging either the upper or lower guide way flanks. In addition, this German patent also describes a sheet guiding plate provided at a small distance below the lower chain guide way and parallel to it, with the sheet guiding plate extending approximately to the front edge of a stapling table. In operation, this sheet guiding plate provides between itself and the sheets conveyed an air cushion which assists in the uniform transport of the sheets and prevents the sheets from having contact with the guide plate.
With such a Z-like or S-like course of a chain guide way as disclosed by the prior art, each change of direction of the chain guide way forces the rolls of the roller chain elements to move from engagement with one guide surface or flank to engagement with an opposed guide surface or flank, with resultant loud noise development in moving from engagement with one guide flank to the other, for instance from a lower chain guide flank to an upper chain guide flank or vice versa. This effect is caused by the inertia of the moving chain mass and the changing centrifugal forces resulting when changing the direction of chain travel, the chain inertia being even greater at points where the gripping pads, which have a considerable mass themselves, are fastened to the chains. Tension imposed on the chains during changing of engaging flanks of the chain guides in the areas where the direction of chain travel changes also can result in considerable noise.
Another disadvantage of prior sheet deliverers is that the mentioned direction changes of the orbitally traveling chains in the Z-like or S-like chain guide ways leads to a wave-like, flag-fluttering movement of the sheets being transported by the gripping pads. This hinders system operating efficiency, particularly when the sheets are printed on both sides, because such fluttering may cause undesired smearing of the freshly printed sheets by their repeated forceful contacting the sheet guides.
After a certain duration of such operation, the repeated change of contact guide flanks and the chain roller elements within the guides leads to premature wear or damage of both the chain rollers and the chain guides, and this results in even greater noise development. Consequently, in a sheet deliverer according to the prior art delivery speed is limited in order to avoid the described disadvantages. In the future, however, sheet deliverers will be needed that can convey or deliver sheets at higher speeds that conventional sheet deliverers due to increasing printing press operating speeds and output.